Liste des communications
Mechanical properties and characterization of metallic bond coat used in hardfacing of petroleum drill bits
Tungsten carbides are widely used as weld hardfacing deposits in petroleum drill bits. To assure proper bonding of the hardfacing to the substrate, several choices of bond coating layers are offered. In this study, tow different commercial powders A and B and mixtures of both them were thermal sprayed onto a carbon steel XC18 substrate used in petroleum drill bits. The micro hardness respectively, of the hardfacing surface and bond coating layers was measured. The microstructure was observed by optical microscopy and field emission scanning electron microscope equipped with energy-dispersive X-ray spectrometry. It has been observed that the mixture of 75% of A and 25% of B produces an uniform coating metallurgically bonded to the substrate with a little heat affected zone and a little amount of porosity. Voir les détails
Mots clés : Thermal spray coating, drill bit, Bond coat layer, weld hardfacing, adhesion.
Restauration d’images radiographiques bruitées appliquées en Contrôle Non Destructif (CND)
La restauration des images dégradées est un problème qui fait partie du domaine de traitement numérique d’image. Lors de l’acquisition des images, les phénomènes tels que le bruit, le flou et la mauvaise qualité sont toujours présents. Notre but est d’atténuer le bruit dans le cas des images radiographiques appliquées dans le Contrôle Non Destructif (CND) pour se rapprocher d’une image plus authentique. Dans notre simulation nous avons considéré un bruit gaussien, nous utilisons : des méthodes basées sur l’utilisation des filtres, des méthodes issues de l’analyse fréquentiel ainsi que des algorithmes de minimisation sans contrainte telles que gradient à pas fixe, ainsi que des algorithmes d'optimisation avec contraintes tel que l’algorithme de gradient projeté, à ses algorithme on applique une régularisation (variation totale) basée sur le model de Rudin-Osher-Fatemi (ROF) utilisant la projection de Chambolle afin d’améliorer la qualité des résultats. A la fin une étude comparative d'algorithmes utilisés. Voir les détails
Mots clés : restauration d’images, variation totale, débruitage
Multiclass Classification of Weld Defects in Radiographic Images Based on Support Vector Machines
In this paper, we present through the experimental study the use of support vector machines (SVMs) in the automatic classification of weld defects in radiographic images. SVM is a machine learning tool used for classification and regression and it is well known for binary classification, but there are many approaches for multiclass classification, the most popular are one versus all and one versus one. The performance of the proposed classification system is evaluated using hundreds of radiographic images representing four types of defects. The experimental results show that the SVM classifier is an efficient automatic weld defect classification algorithm and can achieve high accuracy percent and is faster than multilayer perceptron artificial neural network (MLP-ANN). Voir les détails
Mots clés : Weld defect classification, Support vector machine, one versus all approach, one versus one approach, multilayer perceptron artificial neural network
Automatic Detection and Features Computation of Weld Defects for Radiographic Inspection
In the present paper a part of an automated vision system is introduced. It allows an assessment and features computation of weld defects on digital x-rays images. The vision system contain several steps, the primordial ones are segmentation and feature computation. The segmentation is assured by using a powerful implicit active contour called Local Binary Fitting LBF. In addition the curve is represented implicitly via binary level set function. Such representation has many advantages over the others ones especially in our context. Weld defect features are computed from the segmentation result (final binary level set). We have computed several features; they are ranked in two categories: Geometric features and Statistic features. Such features are very useful in the classification of weld defects and consequently in the radiographic inspection. To validate the implemented algorithm, experiment results on three different images are presented in this paper. Voir les détails
Mots clés : Radiographic inspection, image segmentation, LBF model, Features computation
Evaluation de la Segmentation d‟Images Radiographiques des Joints Soudés
Dans ce travail nous présentons une étude comparative des critères d’évaluation non supervisée de la segmentation. Cette dernière est appliquée sur des images radiographiques des joints soudés dans le but d’extraire le cordon de soudure et le métal de base et de détecter d’éventuels défauts. Dans ce travail, le choix des méthodes non supervisées est justifié entre autres, par la subjectivité liée à la détermination a priori de la région du défaut par l’expert radiographe. Les expérimentations ont permis de comparer ces critères, en termes de crédibilité dans le cas de notre application. Voir les détails
Mots clés : radiographie, joint soudé, évaluation de la segmentation, critère de performance
Numerical Study of Thermal Effects in the Hydrodynamic Behavior of Textured Journal Bearings
The journals bearing characteristics with texture presence on the bearing surface are investigated. The thermal effect has been studied. The used numerical approach in this analysis is Finite Difference Method. The textured bearing performance enhancement passes essentially by a minimum film thickness and a friction torque improvement through an appropriate surface texture geometry and right texture distribution on the bearing surface. It is found that the simulation results are in good concordance with those issued from the litterature. The obtained results by considering the temperature effect are more realisti Voir les détails
Mots clés : Hydrodynamic lubrication, journal bearing, texturation, dimple
Microstructural and mechanical characterization of dissimilar weldedjoint between 2205 duplex stainless steel and API X52 HSLA steel
In this work we study the evolution of the microstructure and phase transformations along the welded joint and the mechanical properties of dissimilar metals weld between duplex stainless steel and HSLA steel. Welds are produced by shielded metal arc welding (SMAW) using a duplex grade filler metal (E2209). The welds obtained in this study, have good mechanical properties, despite the appearance of a hard zone at the interface between the weld metal and the heat affected zone of the HSLA steel Voir les détails
Mots clés : duplex stainless steel, API 5L X52, Dissimilar welding, Heat affected zone
Comparative analysis of surface texturing effect on the performance of hydrodynamic journal bearings
Understanding the influence of surface texturation on journal bearing performances inevitably involves experimental investigations pending being followed by a numerical modeling of the problem. This work consists to model and to understand the evolution of journal bearing characteristics with and without presence of textures on the bearing surface. The numerical approach based on the finite difference method is used in this analysis. Improving performance of textured bearing with spherical dimples suggest that contact characteristics such as minimum film thickness, maximum pressure, and friction torque may be improved through an appropriate surface texture geometry and appropriate texture distribution on the contact surface. The results of our simulations are in good agreement with those obtained experimentally [1]. Voir les détails
Mots clés : Journal bearings, Reynolds equation, Hydrodynamic lubrication, Stribeck curve, texture
Weld Defect segmentation from Radiographic Images using Mumford-Shah Level set Formulation
The limitations of the active contour based on borders have directed the research towards solutions where the contour is built from all the information contained in the image. They are known as region-based active contours. More robust to the noise and less sensitive to the position of the initial curve, the models based on regions have for general principle to develop a curve so that in the convergence, we realize a partition of the image in two homogeneous regions. We obtaintwo regions because a single curve bounds only two domains in image. The region-based active contours base generally on statistical. Voir les détails
Mots clés : Level set, Mumford shah, weld defect.
The texture effect on the static characteristics of hydrodynamic journal bearings
Understanding the influence of surface texturationon journal bearing performances inevitably involvesexperimental investigations pending being followed by anumerical modeling of the problem. This work consists to modeland to understand the evolution of journal bearingcharacteristics with and without presence of textures on thebearing surface. The numerical approach based on the finitedifference method is used in this analysis. The results of oursimulations are in good agreement with those obtainedexperimentally by Xiaobin. Voir les détails
Mots clés : Cavitation, friction, hydrodynamics, Journal bearings, lubrication, numerical analysis, surface texture, Thin films, tribology